The present invention relates to a temperature sensing circuit for sensing temperature. Specifically, the temperature sensing circuit utilizes individually adjustable comparators to determine temperature.
In memory storage devices, densities are steadily increasing and chip areas are being reduced. In addition, operating frequencies are continually increasing. As a result, the energy density introduced into the semiconductor material of the memory systems is increasing. Considerable power loss is generated during the operation of these memory systems. This leads to temperature increases within the semiconductor chips.
Typically, the behavior of the semiconductor chip is affected by temperature increases. For example, in dynamic memory systems such as dynamic random access memory (DRAM) and synchronous dynamic random access memory (SDRAM), memory must be periodically refreshed in order to maintain the charges that represent the stored data. The frequency with which the memory must be refreshed varies with temperature. Consequently, the temperature within the semi-conductor chip must be sensed so that the appropriate refresh rate can be selected.
For low power or mobile or DRAM applications where decreasing current consumption is emphasized in order to increase battery life, various techniques are utilized in an attempt of minimize refresh operation, because it consumes significant current. One such technique is to ensure that the refresh rate does not occur more frequency than required to retain data in memory storage.
Consequently, many applications sense temperature changes in the memory chip so that adjustments can be made to the refresh rate as temperatures vary. For example, the lower the temperature of the device, the lower the refresh rate required to retain data. As the refresh rate is decreased additional power savings is enjoyed.
Various temperature sensing circuits have been employed to sense the temperature of devices in order to make adjustments to the refresh rate. Once such circuit utilizes comparators that compare a sensed temperature to known values in order to determine the level of the sensed temperature. Since relatively small changes in sensed voltage translate to significant changes in temperature, even small amounts of error in these comparators lead to significant errors in sensed temperature. Consequently, an improved sensing circuit would be a useful improvement in the art.